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| Northstar 6 Speed (Page 16/20) |
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Will
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MAR 29, 04:40 PM
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| quote | Originally posted by AJxtcman:
I honed .0015 out of that cylinder.
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Now your bore clearance is twice what it should be.
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AJxtcman
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MAR 29, 08:42 PM
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| quote | Originally posted by Will:
Now your bore clearance is twice what it should be. |
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Specs
Bore---------------------------------------------- 3.6611-3.6617 in
Cylinder Bore Out-of-Round ------------ 0.0039 in
Cylinder Bore Taper ----------------------- 0.0039 in
Piston Diameter ---------------------------- 3.6597-3.6603 in
Piston to Bore Clearance --------------- 0.0008-0.0020 in
Hmmmm I did not hone the scratch out all the way. The bore is still in spec. The new pistons are coated. They are GM replacement pistons. I would have to guess that they are slightly larger than the originals and the Piston to core clearance is still in spec. I did not hone all the wave out of the block.
Bottom line I honed the block and it is not blowing blue smoke.
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Will
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MAR 30, 08:30 PM
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So if the bore clearance was .0015 like it's supposed to be, and you honed the bore .0015, your bore clearance is now .003... with a cast piston.
Take measurements instead of copying and pasting out of the shop manual. You'll build better engines for it.
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AJxtcman
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MAR 31, 01:29 PM
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| quote | Originally posted by Will:
So if the bore clearance was .0015 like it's supposed to be, and you honed the bore .0015, your bore clearance is now .003... with a cast piston.
Take measurements instead of copying and pasting out of the shop manual. You'll build better engines for it. |
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If the spec for taper is .0039" how can the Piston to cylinder spec be .0015? The Spec is listed as .002" correct?
I said I installed the replacement OE coated pistons. Since this is a repair piston could it be .001 larger?
Sorry for hijacking your thread Zac.
I find myself apologizing a lot recently for getting into pissing matches. Sorry again.[This message has been edited by AJxtcman (edited 03-31-2008).]
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Russ544
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MAR 31, 02:43 PM
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| quote | Originally posted by AJxtcman:
If the spec for taper is .0039" how can the Piston to cylinder spec be .0015? The Spec is listed as .002" correct?
I said I installed the replacement OE coated pistons. Since this is a repair piston could it be .001 larger?
Sorry for hijacking your thread Zac.
I find myself apologizing a lot recently for getting into pissing matches. Sorry again.
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one is a mechanic with common sence - one is an engineer without - one builds engines that smoke - one doesn't - huummmmm  [This message has been edited by Russ544 (edited 03-31-2008).]
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Will
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MAR 31, 06:31 PM
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| quote | Originally posted by AJxtcman:
If the spec for taper is .0039" how can the Piston to cylinder spec be .0015? The Spec is listed as .002" correct?
I said I installed the replacement OE coated pistons. Since this is a repair piston could it be .001 larger?
Sorry for hijacking your thread Zac.
I find myself apologizing a lot recently for getting into pissing matches. Sorry again.
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| quote | Originally posted by AJxtcman:
Specs
Bore---------------------------------------------- 3.6611-3.6617 in
Cylinder Bore Out-of-Round ------------ 0.0039 in
Cylinder Bore Taper ----------------------- 0.0039 in
Piston Diameter ---------------------------- 3.6597-3.6603 in
Piston to Bore Clearance --------------- 0.0008-0.0020 in
Hmmmm I did not hone the scratch out all the way. The bore is still in spec. The new pistons are coated. They are GM replacement pistons. I would have to guess that they are slightly larger than the originals and the Piston to core clearance is still in spec. I did not hone all the wave out of the block.
Bottom line I honed the block and it is not blowing blue smoke. |
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The bore clearance is listed as .0008 to .002. A typical blue printing spec for cast pistons is .0015, which falls within the quoted range.
As for how the piston to bore clearance can have a max of .002 while the taper and out of round specs are .0039... that's a question for YOU to answer, if you're going to be using these specs.
What did you use to hone it?
| quote | Originally posted by Russ544:
one is a mechanic with common sence - one is an engineer without - one builds engines that smoke - one doesn't - huummmmm
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You think the first engine I ever tried to overhaul is the only one I've ever built? I thought you had common sense too, Russ. 
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AJxtcman
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MAR 31, 06:55 PM
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My Sunnen hone with 500 stones
I had been using the dealerships Central Tools Bore Gauge, But about a month ago I bought a very nice Mac Tools bore gauge for only $436.98. Wow is it nice. sooooooo much easier to use.
CBG280
Range: 2"-8". Graduation: .0001". Measures cylinder wear. Measuring depth: 12". Self-centering, jeweled indicator. In durable case. Meets JIS B7515 specification.
I have been doing so many 3.6L engines it is unreal[This message has been edited by AJxtcman (edited 03-31-2008).]
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Zac88GT
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APR 02, 03:16 PM
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Well, I just took the heads apart and measured the valve guide clearance and they are perfect. With the valves in the head I siliconed a plate with a barb over the intake and exhaust ports of the cylinders that were burning the most oil. Hooked up my vacuum bleeder and there were no signs what so ever of any leakage past the valve seals or guides. I did find out why #6 had low compression duing my compression tests though. One of the exhaust valves wasn't sealing very well. I had ground the valves and seats so it shouldn't have leaked but i'll relap them and test them before i put it back together. I had ordered a set of pistons from Ontario Reman because they had said that they were in stock in their state side branch. It turns out they were wrong so now they're factory back ordered. I have no idea when i'll get them but hopefully they'll come before the summer is over. If the oil burning isn't the rings than i'm completely stumped. The only places where the engine can really burn oil is either through the rings, the valves, and the PCV system. The valve guides are right in spec and the seals are brand new and sealing great. After pulling the PCV valve out of the valve cover and looking down into the baffle while the engine was running it was totally dry, so it's not the PCV. The only thing left is the rings. The pistons were pretty sloppy, i could rock them back and forth, so it needed new ones anyway. The ring gaps on the new rings were .025 which is double the spec but i've never seen large ring gaps burn oil like this. I'm still stumped but i just hope it's fine when it goes back together this time with new pistons and rings.
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Russ544
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APR 02, 04:09 PM
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I've had no experience on this with the Northstar specifically, but on some engines, if there is not a vaccum in the crankcase, oil will go past even a new and proper sealing set of rings. it's too late to check now, but it might have been enlightening to know if you had a vaccum, or presure, in the crankcase when it was running and pumping oil. but then again, with as much oil as you discribe behind the valves, it sure sounds like it also could have come in via a manifold vaccum port of some kind. pvc or otherwise.
hope you get it worked out,
Russ544
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Will
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APR 02, 08:34 PM
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Can you roll the engine over and get a good look at (or even pictures of) the bore surface finish, especially in cylinders that were burning oil?
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